The invention relates to a reciprocating pump for a high pressure cleaning appliance including a pump housing in which there is disposed at least one pumping chamber having an inlet valve, an outlet valve and a reciprocating piston that projects thereinto in sealed manner, said pump housing comprising a pump block and a pump head which abut closely together at a interface, wherein the pumping chambers and/or the connecting conduits penetrate the interface in sealed manner and, in the region of the interface, accommodate inserts that are insertable into the pumping chambers and/or the connecting conduits from the interface, said inserts being fixed between the pump block and the pump head when in their inserted position.
In the endeavour to make reciprocating pumps for high pressure cleaning appliances ever more compact and lighter, one has repeatedly turned to the idea of making the pump housing out of a synthetic material. However, when constructing high pressure pumps, difficulties have arisen as a result of the very high forces that can occur between the pump block and the pump head in the region of the interface. These are caused by inserts which are inserted into the pumping chambers or the connecting conduits and then clamped between the pump head and the pump block in the region of the interface. Large forces can become effective on these inserts, in the axial direction, due to the high pressure of the medium being pumped, and, in the case of conventionally constructed pumps, these forces have to be accommodated by clamping the pump head and the pump block together. It is thereby necessary to take extensive precautions so as to prevent the pump housing from xe2x80x9cbreathingxe2x80x9d due to the pressure pulsations occurring at the pump rate, for example, the pump heads have to be coated with metal caps.
The object of the invention is to design a reciprocating pump of the kind mentioned in the first part of the main claim in such a way that forces of this nature are avoided in the abutment region of the pump head and the pump block.
This object is achieved in the case of a reciprocating pump of the type mentioned hereinabove in that the inserts themselves and the region of the pumping chambers and the connecting conduits in which the inserts are accommodated consist of a thermally softenable synthetic material, and in that the inserts are connected to the wall of the pumping chamber or the connecting conduit in which they are accommodated by means of a welded joint.
Thus, in contrast to the known constructions, the inserts are not fixed in the pumping chambers and the connecting conduits by clamping them between the pump head and the pump block, but rather, by permanently welding the inserts to the wall of the pump head or the pump block surrounding them.
Furthermore, provision may be made for the pump block and the pump head to consist of a softenable synthetic material at least in the region of the interface and for them to be connected together at the interface by a welded joint. Expensive screw-type fastenings for connecting them together thereby become redundant since the welded bond itself is sufficient to permanently connect the pump head and the pump block together, especially in view of the fact that the forces in the abutment region between the pump head and the pump block are reduced as a result of the inserts being fixed in the connecting conduits and/or the pumping chambers by means of a welded joint.
In another preferred embodiment, provision may be made for the pump housing to comprise a connector used for drawing-off a chemical and incorporating a valve insert which is inserted in a seating of the pump housing, and for the valve insert and the seating to consist of a softenable synthetic material at least in their contact region and for them to be connected together in this contact region by a welded joint. Thus, in this design, the fixing of a valve insert in a seating by a process of welding softenable synthetic materials is not only carried out in the region of the interface, but can also be done for other valve inserts, in this case, a valve insert for drawing-off a chemical .
In accordance with preferred embodiments, the welding of the joint can be executed in various manners, for example, the welded joint may be an ultrasonically welded joint or a butt-welded joint or may be produced by a vibratory process or a frictional process.
In the case of an ultrasonically welded joint, the two parts to be welded are moved against each other at a high frequency but low amplitude, for example, they are rotated against each other about the longitudinal axis of the pumping chamber or the connecting conduit and, as a result of this movement, the heat generated at the point of contact is so great that the synthetic material of both the surrounding wall and the insert melts. The melted synthetic materials intermix and thereby form a dependable welded connection between the insert and the surrounding wall, after they have cooled and thereby consolidated. This welded connection not only has the advantage that the inserts are permanently fixed in their inserted positions in the pumping chamber or the connecting conduit but, in addition, all of the axial forces are accommodated by the welded connection so that these axial forces do not have to be transferred between the pump head and the pump block in the region of the interface, which could lead to the pump housing xe2x80x9cbreathingxe2x80x9d when in operation. Finally, there is provided optimum sealing between the insert and the surrounding wall so that additional sealing means can be dispensed with in this region, for example, there is no longer a need to provide O-ring seals at the outer periphery of the inserts.
In the case of a vibratory welding process, the two parts to be welded are moved against each other at a frequency which is substantially smaller vis a vis that used in ultrasonic welding, this being done by vibrating one of the two parts that are to be welded against the other one. Due to the relative movement and the friction thereby arising between the two parts being welded, heat is generated which leads to a softening of the materials that are to be welded.
One proceeds in a similar manner in the case of the frictional welding process, whereby the two parts being welded are heated up and melt together due to a more or less continuous movement and the frictional heat resulting therefrom.
Finally, in the case of a butt-welded joint, thin heating elements are inserted in the region of the contact faces of the two parts that are to be connected together, these elements being removed after the adjacent materials have melted. The melted materials can then intermix internally and thereby form the welded joint. In the case of an insert that is inserted in a pumping chamber or a boring, the thin heating elements could take the form of a rotary disk shutter for example, these being drawn radially inwardly towards the interior of the insert following the heating of the material whereby they can be withdrawn completely from the insert after the welded connection has been formed.
It is propitious for the insert to be in the form of a sleeve.
In a preferred embodiment, provision may be made for the rim of the sleeve remote from the interface to be in the form of a sealing seat for a valve body. Such a valve body exerts large axial forces on its sealing seat and these forces can be led from the insert directly into the surrounding wall via the ultrasonically welded joint without these forces being conveyed to the respective other part of the pump housing.
It is also propitious, if the sleeve is in the form of a sealing sleeve which projects beyond the interface. The projecting part can then be inserted into corresponding parts of the pumping chambers or connecting conduits in the respective other part of the pump housing and hereby produce a sealing effect in the region of the interface.
In another preferred embodiment, provision is made for the insert to serve as a support for a spring which pushes a valve body against a sealing seat.
Particularly propitious is a design in which provision is made for the insert and the pumping chamber or the connecting conduit accommodating it to have annular shoulders which abut one another when the insert is inserted and which, following the thermal softening of their material by the ultrasonic welding process, become deformed and bond together as the insert is inserted further.
Thus, in such a design, the annular shoulders abut one another in the direction of insertion and these annular shoulders are then heated up in their abutment region due to the micro-movement of the two parts produced by the ultrasonic welding process so that the material in this region melts and intermixes. By pressing on the insert, one will thereby obtain an optimal intermingling of the materials and hence a dependable welded connection which extends axially over practically the whole insertion depth of the insert beginning at the first abutment of the respective annular shoulders of the insert and the pumping chambers or connecting conduit.
It is also possible to work annular grooves into the mutually facing wall sections of the insert and the pumping chambers or the connecting conduits, whereby these annular grooves then serve to accommodate the melted material and, in addition, lead to a solid interconnection of the materials of the insert and the surrounding wall.